Tires are historically prepared with treads of rubber compositions which are comprised of various diene-based elastomers which are often comprised of a combination of cis 1,4-polybutadiene with styrene/butadiene copolymer and/or styrene/isoprene/butadiene copolymer elastomers, although minor amounts of other elastomers may also be present. For some tires such as, for example, load bearing truck tires, the tread rubber may be composed of a significant amount of natural cis 1,4-polyisoprene rubber.
The rubber compositions for various tire components (e.g. tire treads) conventionally contain particulate reinforcing fillers which may be, for example, rubber reinforcing carbon black and/or aggregates of precipitated silica. Such reinforcement fillers are will known to those having skill in such art.
Each of the carbon black and silica particulate reinforcements tend to provide different aspects of physical reinforcement for the diene-based rubber composition. The silica usually requires the aid of a coupling agent to couple the silica to a diene-based elastomer for a more ideal reinforcement of the rubber composition. For example, a precipitated silica conventionally contains hydroxyl groups (e.g. silanol groups) on its surface which is reactive, for example, with an alkoxysilane moiety contained in an alkoxysilane polysulfide based coupling agent.
Sometimes, functionalized silica-treated, or silica modified, carbon blacks are used for the rubber reinforcement which are composed of carbon black which contains silica domains on its surface and where the silica domains contain hydroxyl groups (e.g. silanol groups) on their surface which are, in turn, reactive with an alkoxysilane moiety contained in an alkoxysilane polysulfide based coupling agent. For silica containing carbon blacks, see, for example, U.S. Pat. Nos. 5,679,728, 5,830,930, 5,919,841, 5,948,835 and 6,008,272.
Such carbon blacks which contain silica domains on their surface are envisioned as providing attributes of both carbon black reinforcement and silica reinforcement for diene-based elastomeric rubber compositions. The silica domains may normally be expected to, in turn, contain hydroxyl groups (e.g. silanol groups) on their surface which would be reactive with a coupling agent such as, for example, an alkoxysillane polysulfide based coupling agent. In one aspect, it might be envisioned that if only a fraction of the surface of the carbon black contains the silica domains, then only a somewhat corresponding fraction of a coupling agent (e.g. alkoxysilane polysulfide based coupling agent) need be used to aid in coupling the particulate reinforcement to a diene-based elastomer.
Various amine functionalized styrene/butadiene copolymer elastomers have been suggested for use in rubber compositions for various tire components. For example, see U.S. Pat. No. 6,025,450.
A significant aspect of this invention is the use of silanol functionalized carbon black in combination with an amine functionalized styrene/conjugated diene copolymer elastomer together with an alkoxysilane polysulfide based coupling agent.
In the description of the invention, the term “phr” relates to parts by weight of a particular ingredient per 100 parts by weight of rubber contained in a rubber composition.
The terms “rubber” and “elastomer” are used interchangeably unless otherwise indicated, and the terms “cure” and vulcanize” may be used interchangeably unless otherwise indicated. The terms “compound” and “rubber composition may be used interchangeably unless otherwise indicated.